Just War?: A question from the ignorant

Rob asks:  "On what other basis [besides the presence of WMD tagged for use against the US] could the conflict in Iraq possibly be considered a just war?"  Could the 2003 invasion of Iraq be considered a continuation of the 1991 war with the 2003 invasion caused by Saddam's failure to meet the conditions for cease fire?  I don't know the answer to the question or whether, even if the answer is yes, such a move satisfies the just war criteria.  Any thoughts?

Michael S.